The present invention is directed to a pressure-actuated valve which can be easily modified after installation to adjust the rate of valve operation. The valve is particularly suited for applications involving irrigation systems where clogging by foreign matter in the fluid or variations in supply line fluid pressure require servicing of a restricted inlet port to a valve actuating chamber.
Pressure-actuated valves frequently include a restricted inlet port which transmits a portion of a fluid or gas from the supply line to an actuating chamber for positioning a valve closure member. A vent port from the actuating chamber directs fluid to a control pilot valve for venting to a low pressure area. Because the vent port has a greater capacity than the restricted inlet port, when the control pilot valve is opened, the main valve opens.
Pressure-actuated valves of the prior art, as shown for example, in Griswold, U.S. Pat. No. 3,367,621, and in Williams, U.S. Pat. No. 4,206,901, the disclosures of each of which are hereby incorporated by reference, typically employ a restricted inlet port between the valve input chamber and the valve actuating chamber which is sufficiently small to slow movement of the valve closure member so as to eliminate water hammer and objectionable surge pressures in the supply line. Such restricted passageways, however, are sufficiently small as to be impaired by small particles suspended in the fluid passing into the valve. Such narrow passageways are also sufficiently small as to alter the desired valve closure speed as a result of a changed line fluid pressure condition at the valve site. A modest increase of pressure at a valve site may accelerate valve closure to a rate which creates water hammer and surge pressures in the line. Such a condition, if permitted to continue, can eventually result in excessive wear and tear to the supply line, valves and other line components. Alternatively, a modest decrease in pressure at a valve site may unacceptably slow or prevent valve closure.